The use of so-called safety glazing or penetration resistant glazing for windows, windshields and the like utilizing polycarbonate resin layers as a structural component is well known. For example, glass polycarbonate resin laminates are described in U.S. Pat. No. 3,666,614, the glass and polycarbonate being cohered together using an ethylene-vinyl acetate copolymer. In U.S. Pat. No. 3,520,768, there are described laminates of relatively thick glass having a comparatively thin polycarbonate foil as the cohering material. It is also known to utilize certain polysiloxane-polycarbonate block copolymers described more particularly hereinafter as the adhesive layers. It is normal practice in constructing certain such laminates to utilize glass or relatively hard solid resinous materials as the impact or shock receiving layers while utilizing polycarbonate as the back or inner or downstream layer or that presented to the person or object being protected. In those cases where polycarbonate is used as a layer of a laminate, it is often, because of the relative softness of the polycarbonate, protected, especially on its exposed surface, with a mar- or scratch-resistant and transparency preserving layer usually less than 2 mils thick and, preferably, from about 0.05 to 2 mils thick. The minimum thickness is restricted only by current application technology and the desired durability of the mar-resistant coating. Maximum acceptable coating thickness is a function of the relative brittleness of the mar-resistant finish. In general, such mar-resistant layers, which are well known, can be metal oxides; modified melamines; ultraviolet hardenable organics such as acrylated monomers or mixtures of these monomers with acrylate-modified polymeric resins; inorganic glasses such as silica or alumina; polyurethanes; silicone resins with recurring organic groups such as polymethyl methacrylate; silica, such as colloidal silica, filled silicone resins; silicone resins derived from epoxy terminated silanes; polyamide ester resins; and, ion-beam deposited carbon, among others, are harder and relatively more brittle than the underlying polycarbonate layer which they protect. It has been found that in impact shock-resistant laminates utilizing such relatively brittle material cracks under impact causing the rear-most polycarbonate layer to spall, thereby causing damage to exposed objects behind the laminate. Such spalling occurs because of the so-called " notch sensitive" character of polycarbonates. Thus, if an overlying brittle layer is broken, the fracture lines propagate to the polycarbonate and act as "critical" notches causing the polycarbonate to fail in a brittle manner with little of the energy absorption typical of this normally impact-resistant material.
It will thus be seen that there is a need for providing impact shock resistant laminates using polycarbonate and overlying relatively more brittle material which are reduced in this so-called notch sensitivity, thus making them more useful from a practical point of view.